1. Field of the Invention
The present invention generally relates to the field of image forming devices such as, for example, copiers and printers. More specifically, the present invention relates to optical control for image formation in image forming devices.
2. Description of the Background Art
In the background art, an image forming apparatus such as a laser printer turns a light on and off according to the image data. The apparatus rotates a polygon mirror by a certain number of rotations according to a resolution (recording density) of the image data. The laser light emitted from a laser diode is scanned with a polarized light by the polygon mirror rotated by a motor, and the apparatus forms images by projecting the laser light on a pre-charged photosensitive drum.
After a predetermined time has passed from when the motor was driven in the image forming apparatus, the number of rotations (RPM: rotations per minute) is checked to determine if an error is present by measuring the current flowing in the motor. And when an error, such as a motor lock, is detected by the current flowing in the motor, an error correction process is executed against the error.
Japanese Laid-Open Patent Publication No. 2003-259677 describes an invention in which an ambient temperature of an exposure unit detected by a temperature sensor is compared with a predetermined temperature. If the ambient temperature is higher than the predetermined temperature, an operation environment of the motor is judged to be better than a predetermined level, and thus the period of time between error judgments (i.e. the judgment permission time) is set to a short value. Further, the apparatus does not make an error judgment until a passing time from the output time of a driving control signal to a motor driving circuit reaches the judgment permission time. The apparatus makes an error judgment based upon the passing time and the ambient temperature.
Japanese Laid-Open Patent Publication No. 2002-64927 describes a system that includes a power supply control unit that controls whether electricity is supplied to an electric component, and an electric component control unit outputs a control signal to the power supply control unit. The system monitors a conduction of a power distribution in the electric component, and the system is reset when the system turns on for a period of time that is longer than a preset time. And the system reset is repeated until the electric component reaches a normal operating condition. If the system does not recover when the reset frequency reaches a preset number, an electric power supply is cut off. The interruption control of the power supply to the system is executed by monitoring of the preset time.
Japanese Laid-Open Patent Publication No. H7-294839 describes a timing changing means that changes the detection timing for checking for an error in a number of rotations of a motor. When the rotation of the motor is signaled to stop, the apparatus decides whether it stops the rotation immediately according to the detected number of rotations or whether it reduces the speed of the rotation and then stops the rotation. In the latter case, the apparatus can also restrict the detection of the error for a certain number of rotations.
Japanese Laid-Open Patent Publication No. H8-156316 describes a control of an applied voltage and plural motors. In a standby mode, an applied voltage is 12V. A driving motor is controlled to a number of N3 rotations. In a copy operation mode, at first the driving motor of the first polygon mirror is applied the standby mode voltage, then the applied voltage is increased to 24V and the number of rotations becomes N5 during the writing operation. When a voltage detection unit detects 18 V, the voltage detection unit outputs a detection signal to the control unit. The control unit outputs a voltage supply signal to the second polygon mirror and activates a second driving motor. In the same way, when the applied voltage of the second driving motor becomes 18 V, then a third driving motor of the third polygon mirror is activated. And when the voltage of the third driving motor becomes 18 V, then a fourth driving motor of the fourth polygon mirror is activated. And a rotation of each polygon mirror is increased sequentially to the number of rotations used in an optical writing. Using this method, it is possible to reduce electric power consumption by providing a time lag for the activation of the driving motors, and an operating time of the first copy is stable using such a control system.
Japanese Laid-Open Patent No. 2003-90976 describes a light polarization unit that drives the rotation of rotating parts with mirrors using a motor. The apparatus includes a temperature sensor for detecting a temperature of the motor, a fan for cooling off the motor, and a fan control unit for controlling the number of rotations of the fan. Using this configuration, it is possible to reduce a rise in temperature and to increase the cooling efficiency of the motor by using an air-cooling system. It is further possible to reduce electricity use using an over-speed rotation of the fan.
Japanese Laid-Open Patent Publication No. 2000-3115 describes a mechanical switch that attaches with an apparatus and is activated by an operating part of a process cartridge. The switch detects the process cartridge. The switch cover is closed only when a process cartridge is detected. The apparatus turns a photosensitive drum with a driving gear of an image support unit. Using this configuration, a connection error of connector between apparatus and a non-volatile memory (NVRAM) is eliminated, and it is possible to detect an error of the NVRAM itself.
However, in the above-mentioned background art, an environmental temperature, a passing time, a number of rotations, a changing state of applied voltage, and an error judgment are determined by monitoring an electric component in a motor control of a polygon mirror. These documents do not describe detecting and monitoring an interception state of a power supply voltage applied to the motor from outside. For example, when a power supply voltage (normally +24V) from a power supply to a motor is cut off by some factor, the motor driving unit cannot operate. As a result, a state signal (e.g., a polygon stack signal) becomes an inactive state, and an error outbreak is notified to the system. Further, since the error state is displayed as the error (polygon motor stack error) from the motor drive means, the error in the power supply is not displayed. Accordingly, it becomes difficult to specify a cause of the error.
Furthermore, in the invention described in JP 2000-3115, a notification means stops the operation of the unit and notifies an operator of this state when a process cartridge is not completely loaded. However, this system allows for the detection of only NVRAM. As a result, a control of the other units when errors occur in those other units is not described in the document.